What it means
The kick-down switch state is implausible against accelerator pedal position. Wiring faults of this kind typically come from chafing, water ingress at connector seals, or pin push-back — a wiggle test on the harness while the code is active often confirms the location.
At a glance
- Usually lights the check-engine light
How it works
The kick-down switch tells the transmission that the accelerator has reached its full-throttle request point, and the module checks whether that state agrees with pedal travel. P278B sets when the switch changes state at an implausible point or otherwise fails the expected range and performance relationship, which can reflect switch trip-point drift, pedal travel, or a disturbed sensor element.
Common causes
Most likely first.
- Switch trip point drift
- Accelerator pedal travel out of spec
- Sensor element aged beyond calibration window
Symptoms
- Check engine or transmission warning light may be on
- Kick-down may occur too early, too late, or not at all
- Delayed downshift during hard acceleration
How to diagnose it
- Save freeze-frame data and graph accelerator pedal position alongside the kick-down switch state to see whether the switch changes too early, too late, or inconsistently.
- Inspect the pedal for obstruction, damage, or limited travel, and check that the kick-down switch is correctly mounted in relation to pedal movement.
- Inspect the switch connector and harness for chafing, water entry, pushed-back pins, or loose terminals; gently move the harness while watching the live switch state.
- Test the switch trip point and pedal travel against the manufacturer's specification, checking for a smooth and repeatable transition.
- If the switch and pedal test correctly, trace the signal through the wiring to the transmission control module to find an intermittent connection or implausible input.
Common fixes
- Remove pedal obstructions and correct any mounting issue affecting full travel.
- Repair chafed wiring, water-damaged seals, or pushed-back connector pins.
- Adjust or replace the kick-down switch if its trip point is outside the manufacturer's specification.
- Replace a confirmed aged or faulty pedal-related sensor element.
Can I keep driving?
You can generally drive gently if throttle response is normal, but do not depend on a kick-down downshift for passing or merging. If acceleration or shifting becomes unpredictable, reduce speed and have the fault diagnosed promptly.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.